Project Summary Influenza virus is a major health burden, hospitalizing 200,000, and resulting in 36,000 deaths per year in the United States. Seasonal influenza infection is driven largely by antigenic shift to avoid established antibody responses. Thus, there is a need to create a broadly reactive T cell-based vaccine that recognizes highly conserved internal epitopes, thereby reducing the need for seasonal vaccination. However, the efficacy of cellular immunity to influenza viruses has been shown to wane over time. Lung tissue resident memory T cells (lung TRM) have been found to be critical for this protective cellular response to influenza, and our preliminary data suggests that the gradual decay of lung TRM cell numbers over time is responsible for the loss of cellular immunity to influenza viruses. This project will use a mouse model of influenza infection to examine the loss of subsets of influenza-specific lung CD8 TRM and investigate how this decline is mediated by pro-apoptotic signaling triggered by localized inflammation. This will be accomplished using both respiratory and systemic pathogens to determine if the loss of TRM is specific to the lung or specific to respiratory pathogens. Secondary infections with unrelated pathogens or TLR agonists will be used to examine cell death pathways that drive loss of pre-existing flu-specific TRM. Finally, we will investigate the ability of prime-boost strategies to enhance the longevity of lung TRM. The overall goal of this project is to understand the mechanisms driving the loss of influenza-specific TRM from the lung environment. The knowledge gained in this study will guide future vaccine design against respiratory pathogens by understanding the mechanisms that lead to loss of lung TRM populations, and how localized inflammation affects pre-existing immunity in the lung.